I am having issues spawning a sensor in gazebo 11.

The terminal states that the process has finished cleanly, but no such model appears (whether in rviz or gazebo)

I am able to load my other robot model without issue but am unable to load the sensor.

The launch file code:

 <launch>
  <arg name="paused" default="false"/>
  <arg name="use_sim_time" default="true"/>
  <arg name="gui" default="true"/>
  <arg name="headless" default="false"/>
  <arg name="debug" default="false"/>
  <arg name="verbose" default="false"/>
  <arg name="world_name" default="$(find velodyne_description)/world/example.world"/>
  <arg name="world_name1" default="$(find velodyne_description)/world/wall.world"/>
  <arg name="world_name2" default="$(find velodyne_description)/world/wall2.world"/>

  <!-- set robot starting point-->
  <arg name="x" default="0"/>
  <arg name="y" default="0"/>
  <arg name="z" default="0.00"/>
  <arg name="roll" default="0"/>
  <arg name="pitch" default="0"/>
  <arg name="yaw" default="0"/>

  <!-- Start gazebo and load the world -->
  <include file="$(find gazebo_ros)/launch/empty_world.launch" >
    <arg name="paused" value="$(arg paused)"/>
    <arg name="use_sim_time" value="$(arg use_sim_time)"/>
    <arg name="gui" value="$(arg gui)"/>
    <arg name="headless" value="$(arg headless)"/>
    <arg name="debug" value="$(arg debug)"/>
    <arg name="verbose" value="$(arg verbose)"/>
    <arg name="world_name" value="$(arg world_name2)"/>
  </include>  

  <!-- Spawn the robot -->
  <arg name="gpu" default="false"/>
  <param name="robot_description" command="$(find xacro)/xacro '$(find velodyne_description)/urdf/calibrate.urdf.xacro' gpu:=$(arg gpu)" />
  <node pkg="gazebo_ros" type="spawn_model" name="spawn_velo" args="-urdf -param /robot_description -model calibrator -x $(arg x) -y $(arg y) -z $(arg z) -R $(arg roll) -P $(arg pitch) -Y $(arg yaw)"/>
  <node pkg="robot_state_publisher" type="robot_state_publisher" name="robot_state_publisher">
    <param name="publish_frequency" type="double" value="30.0" />
  </node>

  <!--Spawn sensor-->

  <param name="zed_description" command="$(find xacro)/xacro '$(find velodyne_description)/urdf/zed_spawn.urdf.xacro'" />
   <node name="spawn_zed" pkg="gazebo_ros" type="spawn_model" output="screen"
          args="-urdf -param zed_description -model zed" />

  <!-- RViz -->
  <arg name="rviz" default="true"/>
  <node if="$(arg rviz)" pkg="rviz" type="rviz" name="calibrator" respawn="false" output="screen" args="-d $(find velodyne_description)/rviz/calibrator.rviz" />

The URDF for the sensor:

<robot xmlns:xacro="http://www.ros.org/wiki/xacro" name="zed_spawn">
  <xacro:include filename="$(find velodyne_description)/urdf/zed_stereo.urdf.xacro"/>
  <xacro:arg name="xyz" default="0 0 1.0" />
  <xacro:arg name="rpy" default="0 0 0" />
  <xacro:arg name="hz" default="20" />
  <xacro:arg name="cam_name" default="zed" />

  <gazebo>
      <static>true</static>
  </gazebo>

  <!-- Base Footprint -->
  <link name="base_footprint2">

    <inertial>
      <mass value="0.0001" />
      <origin xyz="0 0 0.5" />
      <inertia ixx="0.0001" ixy="0.0" ixz="0.0"
          iyy="0.0001" iyz="0.0" 
          izz="0.0001" />
    </inertial>

    <visual>
        <origin xyz="0 0 0.5" rpy="0 0 0" />
        <geometry>
            <box size="0.001 0.001 0.001" />
        </geometry>
    </visual>

    <collision>
      <origin
        xyz="0.0 0 0.5"
        rpy="0 0 0" />
      <geometry>
          <box size="0.001 0.001 0.001"/>
      </geometry>

    </collision>
  </link>

  <gazebo reference="base_footprint2">
    <static>true</static>
    <turnGravityOff>false</turnGravityOff>
  </gazebo>

  <zed parent="base_footprint2" name="$(arg cam_name)" hz="$(arg hz)">

  </zed>

</robot>

The zed camera model loads fine when I load it as part of the robot (which is just a flat base with an elevated lidar sensor).